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旁白：听一段动物学课上的演讲。

Narrator: Listen to part of a lecture in a zoology class.

教授：你们今天要读的内容提及到中生代的恐龙化石，中生代大约在6500万年前结束。

Professor: Your reading for today touched on dinosaur fossils from the Mesozoic era, which ended about 65 million years ago.

今天，我们要讨论一下蜥脚类动物。

Today we will be discussing the sauropods.

我想，我们关于蜥脚类动物的讨论会展示出，通过比较化石和当代动物可以学到什么。

I think our discussion of sauropods will illustrate what we can learn by comparing the fossil record to modern animals.

通过化石，我的意思是指史前动物的痕迹，如矿化的骨骼或者留在石头中的骨骼和器官的印记。

By fossils, we mean traces of prehistoric animals such as bones, which become mineralized, or impressions of bones or organs that are left in stone.

现在，蜥脚类动物是曾经存在过的最大的动物之一。

Now sauropods were among the largest animals to exist ever.

他们比蓝鲸更大，蓝鲸是当今存活的最大的哺乳动物。

They were larger than blue whales, which are the largest animals alive today.

他们重达100吨，是大象的20倍。

They weighed up to one hundred tons, twenty times as much as elephants.

而且，他们是极其成功的恐龙种类。

Also, they were an extremely successful kind of dinosaur.

有证据显示，蜥脚类动物在化石记录中存在很长一段时间，超过了1亿年。

There's evidence of sauropods in the fossil record for an unusually long time, over one hundred million years.

那么，为什么蜥脚类动物这么成功？

从生物学上来说，蜥脚类动物不应该这么成功的。

Biologically speaking, sauropods shouldn't have been successful.

像大象这样的大型动物，例如，他们需要更多的食物和能量，比起小型动物有更少的后代。

Large animals like elephants, say, they require much more food and energy and have fewer offspring than smaller animals.

这个使得维持一定种群数量更加艰难。

This makes maintaining a population harder.

当今最大的动物并不生活在陆地上。

The largest animals today don't live on land.

但是，在海洋里更加容易找到食物，比如，一个鲸鱼一天可以吃掉8000磅的事物。

But in the ocean where food is easier to find, a blue whale, for instance, can eat up to 8,000 pounds of food a day.

并且，他们每几年才生产一次。

And they give birth only once every few years.

我们也知道，体温……大型动物不可能轻易地摆脱多余的身体热量。

We also know that body heat, that… well, large animals can't easily get rid of excess body heat.

但是，对于在海里活动的鲸鱼来说，那不是一个问题。

But for an oceangoing whale, that's not a problem.

但是对于一个100吨的陆地动物来说，这可能是个问题。

有好多年我们认为是中生代丰富的植物使得这些巨型动物存活下来。

For years, we have assumed it was the abundant plant life of the Mesozoic that allowed these giants to thrive.

然后，现在我们知道，中生代的氧气水平比我们认为的低的多，蜥脚类动物可以吃的植物比我们认为的要少。

However, we now know that since oxygen levels were much lower in the Mesozoic than we assumed, there was much less plant life for sauropods to eat than we thought.

那么现在，我们正着眼于……我们试图去了解蜥脚类动物的生物学，为了对他们是如何生活有更好的了解，我们将他们的化石和当代动物的身体作比较。

So now, well, we are looking at other… we are, we are trying to understand the biology of sauropods, comparing their fossils to the anatomy of modern animals to get a better idea of how they lived.

我们已经发现的是，蜥脚类动物是保存能量的高手。

What we've found is that sauropods were experts at conserving energy.

它们有巨大的胃部容量，有能力长时间地消化食物，将它以极慢的速度转化为能量，为以后做保留。

They had enormous stomach capacity, the ability to digest food over a long period, converting it to energy at a slower pace, saving it for later.

对于胃很小的动物来说，需要很多能量去不断寻找食物，消化食物。

For animals with small stomachs, it takes lots of energy to constantly look for food and then digest it.

有了较大的胃和缓慢的消化，你不需要那么多的能量了。约瑟夫?

With larger stomachs and slower digestion, you don't need as much energy. Joseph?

学生：事实上，科学家们通过观察……我的意思是，我们通过观察一些远古的骨骼，将它们和我们从当代动物上获知的内容作比较，我们可以获得多少信息？

Student: Does… do scientists actually know about sauropods from looking at… I mean, how much can we actually learn looking at some ancient bones compared to all we can learn from modern animals?

并且，将相差数百万年的动物作比较？

And, comparisons between animals that lived millions of years apart?

好吧，这个似乎……更像是猜测。

Well, it just seems… more like guessing.

教授：在研究灭绝动物的时候是有很多猜测的。

Professor: There's always some guesswork when studying extinct animals.

但是正是那个带来了发现、假设、做出一种猜测。

But that's exactly what leads to discoveries, a hypothesis, a type of guess is made.

我们通过寻找证据支撑来推测假设。

We test the hypothesis by looking for evidence to support it.

然后，有些问题被解决了，这也同样引起了新的问题。

Then some questions are answered, which may lead to new questions.

比如，让我们来看看其中一个比较。

For example, let's look at one of these comparisons.

我们知道蜥脚类动物不能咀嚼食物。

Their skulls show they had no chewing muscles.

很多当代动物，比如鸟类、爬行动物，也不能咀嚼食物。

Lots of modern animals, like birds and reptiles, also can't chew food.

但是，针对消化食物，当代动物有一个很有意思的助手。

But modern animals have an interesting aid for digesting food.

他们吞下石头，食物在胃里被真正消化之前，这些石头被用来帮助磨碎食物。

They swallow stones, stones that are used to help grind up the food before it's actually digested in the stomach.

胃石使得食物更好消化，本质上来说是将食物弄碎，和我们咀嚼食物时做的是差不多的。

Gastroliths make food easier to digest, essentially smashing food up, just as we do when we chew.

随着时间的过去，在动物内部的胃石被磨小，变得更加光滑，圆润。

Over time, gastroliths inside the animal are ground down and become smooth and rounded.

现在，蜥脚类动物化石常被发现有光滑的石头。

Now, sauropod fossils are commonly found with smooth stones.

有很多年我们认为这些石头是胃石。

For years we thought these were gastroliths.

他们看上去就像是胃石，并且在蜥脚类动物的胃部被发现。

They look just like gastroliths and were found in the area of the sauropods' stomachs.

一个最近的研究测量了现代动物，鸵鸟中胃石的大小。

A recent study measured the gastroliths in modern animals, in ostriches.

研究显示鸵鸟需要咽下他们体重百分之一的胃石。

And the study showed that ostriches need to ingest about one percent of their total body weight in gastroliths.

但是，我们能够确定，在蜥脚类动物里发现的石头总数非常不成比例，比他们百分之一体重的十分之一还少。

But we have been able to determine that the stones found with sauropods totaled much less proportionally, less than a tenth of one percent of their body weight.

所以，现在我们不是很肯定这些蜥脚类动物石头是用来干嘛的。

So now we are not quite sure what these sauropods' stones were used for.

这可能是他们在觅食的时候不小心误食的，它们并没有任何的作用。

It could be they were accidently ingested as the sauropods foraged for food, that they served no real purpose.

其他的研究人员推测蜥脚类动物吞食这些石头，是将它们作为他们所需矿物质的来源，比如说钙。

Other researchers speculate that sauropods ingested these stones as a source of some the minerals they needed, such as calcium.

那么，起初在蜥脚类动物发现的时候是胃石的假设，尽管这个没有得到支持，已经帮助我们去做出新的假设，这可能最终会将我们引向正确答案。

So the original hypothesis that the stones found with sauropods were gastroliths, even though it hasn't been supported, has helped us to make new hypotheses, which may eventually lead to the answer.

What point does the professor make when she compares blue whales to large land animals?

According to the professor, what recent finding about the Mesozoic era challenges an earlier belief?

Compared to small animals, what disadvantages do large animals typically have?

Why does the professor discuss gastroliths that have been found with sauropod fossils?

What did researchers conclude from their study of sauropods and gastroliths?

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